The present invention relates to derailleur and more particularly to an automatic derailleur which is adapted to speed change so as to more effectively save labor of a rider.
A bicycle equipped with derailleur is well known. However, such conventional bicycle suffered from several disadvantages. For example, a rider cannot manually operate a gear selector in time when a road condition has changed. For example, a flat road has changed into an uphill road. As such, the rider has to spend more labor in riding. Moreover, for most riders they cannot suitably operate the gear selector due to lack of experience and/or complicated operating procedure. There are some available bicycles are equipped with automatic derailleurs. However, they are relatively expensive and the derailleur is comprised of too many components, thus bulky. Additionally, there are still some available bicycles equipped electronic automatic derailleurs. However, as known that rain may rust the bicycle as well as the electronic automatic derailleur since there is no or little protection of the derailleur. As a result, it is susceptible to being malfunctioned. Thus improvement exists.
It is therefore an object of the present invention to provide an automatic derailleur device adapted to a speed change of a bicycle comprising derailleur means mounted to a frame adjacent a hub of a rear wheel and comprising an arm, a sprocket roller meshed with one of a set of different-sized sprocket wheels on the rear wheel; control means comprising a control member and a lower tension wheel meshed with an endless sprocket chain wherein the tension wheel is coupled to the control member and secured to one end of the arm by a fastener respectively and the control member is coupled to both a control cable and the frame; a hydraulic cylinder comprising a shaft having a large outer cylindrical section secured to the other end of the arm and a small inner cylindrical section, a collar at a junction of the outer and the inner cylindrical sections, an elastic member put on the large outer cylindrical section and biased between the collar and an inner wall of the hydraulic cylinder, and a hollow cylindrical block with the small inner cylindrical section passed through; and a pump enclosed by the hydraulic cylinder and comprising a piston rod extended through the hydraulic cylinder to rotatably couple to the sprocket roller, a plurality of blades radially extended from the piston rod and abutted on the other opposite inner wall of the hydraulic cylinder, and a cylindrical passage formed between a portion of an inner surface of the hydraulic cylinder and the hollow cylindrical block, the passage served to communicate oil between the hydraulic cylinder and the pump. Whereby in a stop or low speed of the bicycle, a largest one of the set of sprocket wheels is meshed between the sprocket chain and the sprocket roller, the elastic member is expanded to bias the collar inward to urge against the hollow cylindrical block by its stored energized force, the small inner cylindrical section of the shaft is actuated to move to compress an oil stored in the pump to flow to the hydraulic cylinder through the passage, and the other end of the arm is proximate an outer surface of the hydraulic cylinder. Alternatively in an acceleration of the bicycle, the oil in the hydraulic cylinder is sucked to flow to the pump through the passage by a rotation of the blades which is in synchronism with the rotating sprocket roller, the small inner cylindrical section of the shaft is forced to move outward by the oil in the pump, the elastic member is compressed outward by the collar, the large outer cylindrical section of the shaft is actuated to extend outward from the hydraulic cylinder, the other end of the arm moves away from the outer surface of the hydraulic cylinder, and a smaller one of the set of sprocket wheels is meshed with the sprocket chain and the largest one of the set of sprocket wheels is meshed with the sprocket roller respectively.